IBM's alphaWorks has released XML Bridge for SAP, software to provide XML integration between SAP R/3 systems on the one side and arbitrary SAP R/3 or non-SAP systems on the other side.

The software is aimed at those who want to provide loose coupling between SAP R/3 and outside systems, want to support communication with systems through a firewall (via SOAP) or want integration with MQseries.

The website describes the architecture:

... we have defined a generic architecture to support plugging in different infrastructures for XML exchange. This allows it to extend the bridge by adding plugins for arbitrary transmission middlewares. The standard set of plugins covers HTTP and MQSeries. The bridge is designed to support synchronous, asynchronous and transactional RFCs, BAPIs and IDocs.

Regarding compatibility with SAP R/3, IBM's FAQ has this to say:

Although not all different versions of SAP R/3 have been tested explicitly we expect no problems on all releases correctly supporting BAPIs and RFCs. To our current knowledge these are all systems newer then release 3.1G except 4.0A.